1. Field of the Invention
The invention relates to a device and method for damping mechanical vibrations of printing presses.
The drive train of a printing press with the parts connected thereto, such as cylinders and rollers, for example, constitutes a system having dynamics which are determined by spring constants, moments of inertia, rotating and oscillating masses, and so forth. The rotating parts of this driven drive train can be excited to vibrations due to the following effects: angle-dependent effects, i.e. synchronous oscillations, recurring over one rotation and effects which do not recur periodically with one rotation, are to be considered as distinct. Recurring load moment deviations, such as are generated, for example, by cam transmissions or by the failure of single or n-revolution gears are to be counted with the angle-dependent, i.e., synchronous, vibrations. Aperiodic or non-cyclical vibrations recurring with one rotation, i.e., asynchronous vibrations, can be produced, for example, by periodic excitations deviating from the rotational frequency. They occur, for example, when belts are used, due to vibrator shock or stroke, or due to errors or failure of half-rotation gears. Aperiodic noise phenomena, such as from ink separating from paper or effects of paper pulling, for example, cause asynchronous vibrations. Furthermore, vibrations can be produced in the system due to parameter deviations which, in comparison with the sheet travel, exhibit a slight change in velocity (for example, oil temperature deviations, which have an effect upon basic friction).
Many angle-synchronous disturbance have a high excitation energy. The periodic vibration shapes over one rotation which result therefrom do not, however, have any noticeable effect upon the printing quality with respect to ghosting in the printed image, because the rotating parts of the printing press always assume the same angular position at the instant of paper transfer or acceptance. Asynchronous disturbances become noticeable, however, in the printing quality. They cause ghosting because the angular position of the rotating parts of the printing press is subject to deviations during sheet transfer. The effect of these disturbances becomes noticeable due to their most often low excitation energy essentially when characteristic or natural frequencies of the printing press are excited, wherein the damping is low. The relatively slow parameter deviations mentioned hereinbefore have no effect upon the ghosting.
It has become known heretofore, for the purpose of reducing mechanical vibrations, to reinforce the side walls of the printing press and/or to install reinforced gears as well as other reinforced components. These measures are expensive, increase the weight of the printing press and do not always produce the desired results.
It is accordingly an object of the invention to provide a device and a method for damping mechanical vibrations of printing presses which improves the printing quality.